1. Field of the Invention
The present invention relates generally to an actively controlled suspension system for an automotive vehicle for actively controlling suspension characteristics according to vehicle driving conditions for achieving both of riding comfort and driving stability. More specifically, the invention relates to a fail-safe system of an actively controlled automotive suspension system which can perform fail-safe operation in response to failure in a sensor for monitoring the vehicular driving condition.
2. Description of the Background Art
Actively controlled suspensions have been developed and proposed in various constructions. In the recent days, such actively controlled suspension systems are known as good suspension systems for achieving both of riding comfort and vehicle driving stability. In general, such actively controlled suspension system performs anti-rolling suspension control, anti-pitching suspension control, bouncing suppressive suspension control, road shock absorbing suspension control and so forth. The suspension control system includes a plurality of sensor means for monitoring the vehicular driving condition. Since the suspension control for adjusting stiffness or suspension characteristics depending upon the suspension control parameters monitored by the sensor means, failure of the sensor means directly results in malfunctioning of the suspension control. Therefore, in case of failure of the sensor means which causes error in the monitored vehicular driving condition data, fail-safe operation has to be performed for controlling suspension system to predetermined suspension mode for assure safety.
In detection of failure of a sensor which monitors bounding and rebounding motion of the vehicular body in relation to a suspension member which rotatably supports a road wheel, a difficulty is encountered in discrimination of normal sensor condition and abnormal sensor condition. Namely, in the event that the vertical displacement monitoring sensor outputs a sensor signal representative of extraordinary magnitude of vertical displacement, discrimination whether such extraordinary value is caused by failure of the sensor or by vehicular driving condition, such as bottoming caused by passing over relatively large uneveness on the road, can not be made.